During scheduling of periodically executing real time processes in the operating system of a computer system, the temporal resolution is usually directly dependent of the resolution of the clock with which the process is periodically scheduled. In for example control systems exploiting real time processes with absolute reference time, an erroneously computed time results in negative consequences. Often several points in time are computed during one control cycle. Assume a control system operating with three parameters of time. During scheduling of the real time processes the following holds true:    for each control cycle, three points in time are established which shall be scheduled relative to the current cycle (relative time);    the control process, performing the calculation of the three points in time, runs periodically;    an absolute reference time is demanded;    the temporal resolution with which the process scheduled three times per control cycle is of a given size, for example 1 μs;If the clock frequency is drifting from its intended value, which all clock's frequency does to a certain extent, the error added to the computed points in time for the three parameters of time will constantly increase. The result is that a control deadline will be missed which will cause deteoriated control performance in the best case, or machine failure in the worst case. This means that the such a process works in so called hard real time.
One purpose of the present invention is to make available a method for scheduling real time processes with absolute reference time.